"Medical futility" may be provisionally defined as a medical conclusion that a therapy is of no value to a patient and should not be prescribed. The current debate about medical futility is one of the most important and contentious in medical ethics. Proponents believe that allowing physicians to determine and withhold futile therapies can be done without disturbing the current paradigm of medical ethics which respects patient autonomy with regard to informed consent and the right to refuse treatment. Others conclude that medical futility is simply an unacceptable form of medical paternalism. Some adopt a middle position that doctors can predict medical futility; they believe that attempting this does not necessarily justify imposing decisions to forgo life-sustaining therapy on patients. Regardless of its policy outcome, this important debate is leading to a reexamination of the nature of a patient's entitlement to health care and of the ends of medicine. It has two aspects. A definitional debate examines the concept of medical futility and its derived clinical criteria. A second debate considers the nature of the authority and procedures to act on the conclusion that a therapy is futile by withholding or withdrawing treatment.